import java.util.Stack;

class MyQueue {

    public Stack<Integer> s1;
    public Stack<Integer> s2;
    public MyQueue() {
        s1=new Stack<>();
        s2=new Stack<>();
    }
    
    public void push(int x) {
        s1.push(x);
    }
    
    public int pop() {
        if(empty())return -1;//两个栈都是空，队列为空
        if(s2.empty()) {
            while(!s1.empty()) {
                s2.push(s1.pop());
            }
        }
        return s2.pop();
    }
    
    public int peek() {
        if(empty())return -1;//两个栈都是空，队列为空
        if(s2.empty()) {
            while(!s1.empty()) {
                s2.push(s1.pop());
            }
        }
        return s2.peek();
    }
    
    public boolean empty() {
        return s1.empty() && s2.empty();
    }
}